1. Field of the Invention
This invention relates to a brake band for use in a transmission for a vehicle such as an automobile, an agricultural machine or a construction machine, and particularly for use in an automatic transmission. More particularly, it relates to a brake band capable of floating the opposite end portions of a strap twined around a drum by a predetermined amount from the surface of the drum to thereby prevent any sudden torque fluctuation during the tightening of the brake band.
2. Related Background Art
In an automatic transmission, a multiplate clutch, a brake band or the like is used to effect speed change with an input element such as a gear train fixed and liberated. Of these, the brake band is widely used because it has the characteristic that its braking force differs depending on the braking direction of a drum even when the same acting force is applied and it has the preferred characteristic of smoothening upshift.
The construction of a brake band according to the prior art has been as follows.
The strap of the brake band is wound on a drum and brackets are provided on the opposite end portions thereof. An anchor pin and an apply pin are slidably or swingably supported on each bracket. Also, the end portions of the strap on which the brackets are provided are in light contact with the outer peripheral surface of the drum during the non-operation of the brake band (during the non-tightening when a tightening force is not applied to the drum).
In such a construction, the operational force of the apply pin urges the strap having a lining attached to its back against the outer peripheral surface of the rotating drum through the bracket. Thereupon, a frictional force created is transmitted as strap tension to the anchor pin through the bracket on the anchor side. The frictional force transmitted to the anchor pin is received by the case of the automatic transmission and appears as a torque. When a great torque is suddenly transmitted, a great speed change shock will occur. For example, when the brake band is incorporated in an automatic transmission used in a vehicle such as an automobile, this speed change shock becomes great enough to be bodily sensed and thus, gives an unpleasant feeling to the crew.
The problem of the speed change shock by the sudden transmission of a great torque arises from the fact that during a low load, the brake band has a greater torque capacity than necessary. The present invention has been made in view of the problem as noted above.